Thisisanimportantproblem_______toofewsocialscientistshaveresearched.A.whichB.thatC.intothatD.intowhich
正确答案:Dintowhich引导的是problem的定语从句。which指代problem,into与research搭配。 (本解析由

Thisisanimportantproblem_______toofewsocialscientistshaveresearched.A.whichB.thatC.intothatD.intowhich
正确答案:D